As someone who has read the post numerous times and feels somewhat knowledgeable about it, I believe I can explain all 4 of these points.
Only certain hand-picked individuals will be given the right to craft one of these weapons, so they will most likely be good RPers and candidates to regulate said weapons.
There are red-lines all across the board for these guns and they have a uniquely designed rolling system that ensures no one could power-game without getting in trouble. The players still need to report if they do see power-gaming, and it is not a craft/magics fault if there is power-gaming, the players are to blame for their mistakes.
This system, like I said, has a rolling system that is strict and unforgiving, there is a baseline for how strong they are, and it only goes down.
Steel Plate armor will counter most of these weapons, with exception to the castor that works like a shot-gun. The farther you are from the gun, the less damage you will receive from the bullet.